The present invention relates generally to the packaging of electronic components. More particularly, the present invention relates to an image sensor package.
Image sensors are well known to those of skill in the art. An image sensor included an active area, which was responsive to electromagnetic radiation. To avoid obstructing or distorting the electromagnetic radiation which struck the active area of the image sensor, it was important to avoid contamination, e.g., from dust, of the active area.
Image sensors were fabricated from a silicon wafer. More particularly, a plurality of image sensors were formed in a single silicon wafer. The silicon wafer was singulated, sometimes called cut-up or diced, to separate the image sensors from one another. However, during this wafer singulation, silicon shards were generated. These silicon shards had a tendency to contaminate and scratch the active areas of the image sensors. As a result, image sensors were damaged or destroying, which undesirably decreased the yield. However, to reduce cost, is important to have a high yield.
The singulated image sensor was then used to fabricate an image sensor assembly. In one conventional assembly, the image sensor was located within a housing, which supported a window. Radiation passed through the window and struck the active area of the image sensor, which responded to the radiation.
More particularly, the image sensor was mounted to a printed circuit mother board. After the image sensor was mounted, the housing was mounted around the image sensor and to the print circuit mother board. This housing provided a hermetic like seal around the image sensor, while at the same time, supported the window above the image sensor.
As the art moves to smaller and lighter weight electronic devices, it becomes increasingly important that the size of the image sensor assembly used within these electronic devices is small. Disadvantageously, the conventional image sensor assembly described above required a housing to support the window and to hermetically seal the image sensor. However, this housing was relatively bulky and extended upwards from the printed circuit mother board a significant distance, e.g., 0.100 inches (2.54 mm) to 0.120 inches (3.05 mm) or more. As a result, the image sensor assembly was relatively large.
Another important characteristic of an image sensor assembly was the temperature at which condensation formed within the housing of the image sensor assembly, i.e., the dew point of the image sensor assembly. In particular, it was important to have a low dew point to insure satisfactory performance of the image sensor assembly over a broad range of temperatures.
In accordance with the present invention, an image sensor package includes an image sensor having an upper surface with an active area and bond pads formed thereon. A noncritical region of the upper surface is between the active area and the bond pads. A window overlies the active area and is supported on the noncritical region by a window support.
The window, window support and image sensor define a sealed cavity and the active area is located within the cavity. In particular, the active area is located within the cavity, which is sealed to protect the active area against external moisture, dust and contamination.
Recall that in the prior art, a window was supported above an image sensor with a housing. This housing was typically formed of ceramic, which was relatively expensive. Advantageously, the image sensor package in accordance with present invention eliminates the need for a housing of the prior art. Accordingly, the image sensor package is significantly less expensive to manufacture than image sensor assemblies of the prior art.
Further, since the window is attached directly to the image sensor by the window support, a distance, sometimes called the Z height, between the window and the upper surface of the image sensor can be made relatively small. As a result, the image sensor package can be made relatively thin compared to a prior art image sensor assembly.
In contrast, the housing of the prior art image sensor assembly was relatively bulky and extended upwards from the printed circuit mother board a significant distance. Since the image sensor package in accordance with the present invention can be made relatively thin, the image sensor package is well suited for use with miniature lightweight electronic devices, which require thin and lightweight image sensor assemblies.
Further, since the Z height is relatively small, the volume of the cavity is also relatively small. By minimizing the volume of the cavity, the amount of any moisture trapped within the cavity is also minimized. This, in turn, essentially eliminates the possibility of moisture condensation on the interior surface of the window or on the active area of the image sensor. As a result, the image sensor package in accordance with the present invention has a very low or nonexistent dew point.
In contrast, prior art image sensor assemblies had a significant dew point, i.e., a temperature at which condensation formed within the housing, which enclosed the image sensor and supported the window. Since the housing was relatively bulky and held a relatively large volume of air, moisture had a tendency to get trapped within the housing and to condense on the interior surface of the window or on the active area of the image sensor.
To avoid this condensation, it was important to avoid subjecting the image sensor assembly to extreme low temperatures. Disadvantageously, this limited the temperature range over which the image sensor assembly would satisfactorily perform. Alternatively, the image sensor assembly was fabricated in a low humidity environment to avoid trapping moisture within the housing and was hermetically sealed by the housing to keep out moisture. This added complexity, which increased the cost of the image sensor assembly. Further, in the event that the hermetic seal of the housing failed, the image sensor was damaged or destroyed.
Since the image sensor package in accordance with present invention has a very low or nonexistent dew point, the image sensor package operates satisfactorily over a broader range of temperatures and, more particularly, at lower temperatures than image sensor assemblies of the prior art.
Also in accordance with the present invention, a method of fabricating a plurality of image sensor packages in an array to reduce cost is presented. The method includes applying a bead to a noncritical region of an upper surface of an image sensor, the upper surface including an active area and bond pads, the noncritical region being between the active area and the bond pads. A window is mounted to the image sensor with the bead.
In one embodiment, the image sensor is one of a plurality of image sensors integrally connected together. In accordance with this embodiment, the method further includes singulating the plurality of image sensors.
Of importance, the active areas of the image sensors are protected by the windows (in combination with the window supports) during singulation. More particularly, the windows protect the active areas from contamination and scratching during singulation, e.g., from silicon shards. The windows also protect the active areas during subsequent processing of the image sensor package, e.g., during subsequent wire bonding and/or encapsulation and/or molding. As a result, damage or destruction of the image sensors is avoided. Accordingly, yield is increased and package cost is reduced compared to the prior art.
Further, by forming a plurality of image sensor packages simultaneously, several advantages are realized. One advantage is that it is less labor intensive to handle and process a plurality of image sensor packages simultaneously rather than to handle and process each image sensor package on an individual basis. Another advantage is that usage of materials is more efficient when an array of image sensor packages is fabricated. By reducing labor and using less material, the cost associated with each image sensor package is minimized.